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Pitting on the inner ring of a rolling bearing. Recorded at the Institute for Materials Science and Applied Mathematics at the TH Köln
Crack parallel to the surface in the section. Recorded at the Institute for Materials Science and Applied Mathematics at the TH Köln
Near surface cracks at about 45 ° to the surface. Recorded at the Institute for Materials Science and Applied Mathematics at the TH Köln
Scanning electron micrograph of a Pittinggrübchens. Recorded at the Institute for Materials Science and Applied Mathematics at the TH Köln

As pitting (in German: pitting ) a cup-shaped material outbreak case of alternating force is referred to, by the near-surface micro-cracking is caused. This damage process occurs primarily in the area of ​​classic mechanical engineering , for example with roller bearings and gear wheels .


Pitting is caused by the formation of fatigue cracks as a result of millions to billions of times alternating, mostly swelling loads. The fatigue usually begins in the zone of highest shear stresses parallel to the surface. As a result of the Hertzian pressure, this lies at a characteristic depth of a few tenths of a millimeter below the surface. The stress peaks can reach 3000 N / mm². By structural inhomogeneities, porosities or non-metallic inclusions occurring notch effect caused in the zones of maximum shear stresses, formation of micro-cracks parallel to the surface. These spread to the surface and cause the material to break out like a shell. In the case of roller bearings, the breakouts are rolled over, which leads to local stress peaks and thus to an acceleration of the damage process. Furthermore, there is also a plastic flow on the surface, in the direction of the main shear stress at 45 ° to the surface. This creates microcracks on notches on the surface. They spread out along the main shear stress direction at 45 ° to the surface.

Other influencing factors

Other influencing variables in addition to Hertzian pressure are, for example, the surface hardness and the hardening depth, the surface quality, the viscosity and additives of the lubricant, the temperature stress as well as possible flank shape errors and, in the case of gears, the peripheral speed.


The formation of pits can be prevented by constructive measures. The “right” material , the “right” heat treatment and the “right” manufacturing process should be used for the respective application. The values ​​of the permissible surface pressure (boundary surface pressure ) recognized in mechanical engineering for the selected material must not be exceeded. This can be ensured by numerical calculation of the components. Optimizing the sealing systems or improving the filtering of the lubricant as well as generally using an optimally suitable lubricant are further measures to reduce the risk of pitting. Furthermore, regular testing and proper maintenance and servicing of the machines and machine elements concerned should be carried out in accordance with the manufacturer's specifications.

Individual evidence

  1. SCHATT Werner., SIMMCHEN E., ZOUHAR G .: Construction materials of machine and plant construction. Deutscher Verlag für Grundstofftindustrie Stuttgart, 1998, p. 421.
  2. DAHLKE Hans: Handbook rolling bearing technology. Vieweg Braunschweig, 1994, pp. 224, 239ff.
  3. ESCHMANN Paul: The capacity of rolling bearings-an assessment based on new points of view. Springer Verlag Berlin / Göttingen / Heidelberg, 1964, p. 4ff.
  4. GLÄSER Heinz: Damage to sliding and roller bearings. Verlag Technik Berlin, 1990, pp. 75ff, 81.
  5. Digression into the fundamentals of contact mechanics Accessed online on January 27, 2018 at 9:55 a.m.
  6. a b Pitting - risk factor for gear failure . Online at www.rewitec.com; accessed on July 27, 2017.
  7. Damage types - pitting . Online at www.nskeurope.de; accessed on July 27, 2017.